1. Technical Field
This invention relates to a location measuring device and a location measuring method. More specifically, this invention relates to such a location measuring device and a location measuring method that obtain three-dimensional coordinates of a camera or an object from motion images of the object photographed by moving the camera relative to the object.
2. Related Art
There is a technique to measure the location of an object or a camera itself using images of the object which the camera picks up in succession while the camera makes motion relative to the object. With this technique, a plurality of images are photographed at a distance and corresponding points between the images are tracked, a stereo pair is set up from two of the images, model images are made, and bundle adjustment is made on the basis of the plurality of images to obtain final and three-dimensional measurement results. Such a technique is disclosed for example in the Patent Document 1.
[Patent Document 1] JP-A-2007-183256
The conventional technique described above is constituted to include the steps of: extracting feature points from a shot image, tracking in real time candidate points corresponding to the feature points on a plurality of images photographed before and after taking the shot image, determining the corresponding points from the tracked result, and calculating coordinates of the camera location or the object location using the determined corresponding points. This process includes, as will be described later, the following operation steps: relative orientation to determine a model coordinate systems so that two images forming a stereo pair satisfy specific conditions (such as coplanar condition, colinear condition, vertical parallax removal condition, etc.), and bundle adjustment for adjusting a plurality of model coordinates to determine the travel of the camera. The above processes and calculation steps respectively are accompanied by calculating operations to determine likable coordinate values and coordinate transformation parameters from a large number of observation data containing errors. Conventionally, the above calculations have often used the least squares method.
However, there are problems as described below: If feature points have incorrect corresponding points in finding three-dimensional coordinates of the camera itself or the object, there may be cases in which the three-dimensional coordinates are not determined accurately, and moreover the solution does not converge in the process of calculation, leading to inability of tracking. The error in the tracking section occurs for example when corresponding points, which are incorrect or inappropriate for calculation (for example, points (tree leaves or the like) that are moving gently, quasi corresponding points or points that feigns to be coincident), are included. In that case, calculation in later steps deteriorates in accuracy and, in the worst case, the solution does not converge. Similar situation occurs also when a stereo pair containing many of such points is chosen. When convergence of solution deteriorates, calculation speed decreases. Even if model coordinates are calculated successfully and bundle adjustment is applied while they contain errors, accuracy may deteriorate due to insufficient removal of large errors. Besides, if large errors remain or some points remain with large errors, estimating calculation using the least squares method consequently takes much time for convergence, and real time processing cannot be carried out.
Therefore, the object of the present invention is to provide a device and a method that make three-dimensional measurement of the location of an object or the apparatus itself at a high speed and with a high accuracy.